This invention relates to the production of helically wound coils and, more particularly, to an apparatus for the manufacture of edgewound magnetic stator cores for dynamoelectric machines.
Stator cores of dynamoelectric machines, such as electric motors, generators or alternators, are commonly produced by stamping annularly shaped laminations from thin sheet metal and stacking these laminations together to form a cylindrical core with a central bore of a shape and size suitable to receive an associated rotor member. It is well known to those skilled in the art that this method is uneconomical because of the significant amount of scrap material that results from punching a plurality of circularly shaped objects from sheet metal.
It is also well known that significant material savings can be achieved by utilizing a continuous strip of magnetic material and helically rolling or forming it into the above-described cylindrical core shape. The idea of rolling or forming strip material on edge to form a helical coil is disclosed in U.S. Pat. No. 1,032,925 issued to Miller on July 16, 1912 which employs rigid guides to force a generally straight strip of material into a circular, edgewound shape. U.S. Pat. No. 1,920,144 was issued to Fisher on July 25, 1933 and discloses a combination of a punch press and a helical winding machine which also utilizes an arcuately shaped shoe to bend the strip material into a helical coil. The shoe, which is functionally similar to one described in Miller, exerts a force on one edge of the strip material and radially forces it to bend into a circular shape.
The use of forming shoes or guides, as described in both Fisher and Miller, is also disclosed in U.S. Pat. No. 3,464,101 issued to Zubal et al. on Sept. 2, 1969; U.S. Pat. No. 3,283,399 issued to Hart et al. on Nov. 8, 1966; U.S. Pat. No. 3,206,964 issued to Hart et al. on Sept. 21, 1965; U.S. Pat. No. 3,243,623 issued to Hart et al. on Mar. 29, 1966 and U.S. Pat. No. 3,062,267 issued to Hart et al. on Nov. 6, 1962. These devices, which utilize shoes, or guides, to form the helical coil, pull the strip material in such a way as to force one of its edges against the shoe. This contact forces the strip into a circular shape by guiding it around an axis of rotation, thus forming a helical coil.
Another technique used to form a helical, edge-wound coil is to use pressing rollers to deform one edge of the strip in such a way as to reduce its thickness and therefore elongate it in a direction along its length. Since one edge is thus made longer than the other, the strip naturally tends to form into a curled shape. By continually thinning one edge in this way, the strip material is caused to bend into a generally helical shape. This technique is disclosed in U.S. Pat. No. 2,437,500 issued to Bruegger on Mar. 9, 1948; U.S. Pat. No. 1,920,154 issued to Carlson on July 25, 1933; U.S. Pat. No. 2,845,555 issued to Carpenter et al. on July 29, 1958 and U.S. Pat. No. 3,845,647 issued to Cockin on Nov. 5, 1974.
A somewhat similar technique is described in U.S. Pat. No. 4,193,281 issued to Kulikov et al. on Mar. 18, 1980. It utilizes a pointed shaping member that impresses a series of indentations along one edge of a strip of material in such a way as to elongate that edge and cause the curling of the strip to occur in a way similar to that achieved by the pressing roller method described above.
In order to cause the strip of material to travel in a circular path, some devices are equipped with a plurality of pins that fit into slots that have been prepunched into the strip. These pins are attached to a rotating disc and, once inserted into the slots, pull the material in a circular motion to form a helical coil. Devices that utilize pins in this way are described in Kulikov, Rediger, Zubal and the four patents of Hart et al. described above.
It has been found that the techniques described above are unable to produce cores in which the inside and outside diameters and axial tooth registration are consistent with stringent design tolerances. It is therefore an object of the present invention to provide a means for producing helical, edgewound cores that are dimensionally accurate.